Radar (Radio detection and ranging) is to find the existence of a target using an electromagnetic signal that is radiated to and then is reflected from the target. As radio waves used in the radar, microwaves having a wavelength of 30 cm or less may be used. The reason why the microwaves having the wavelength of 30 cm or less is used in the radar is that as the wavelength becomes shorter, linearity, directivity, and sensitivity of the radar become better.
Antennas used in the radar may include a Vivaldi antenna, an LP (Log Periodic) antenna, an IR (Impulse Radiation) antenna, a TMP (Transverse Electro Magnetic) horn antenna, and a resistive dipole antenna. The antennas used in the radar have common features. The antenna used in the radar has a low center frequency, and thus superior penetration performance can be obtained through a medium. Further, the antenna used in the radar operates in a wide bandwidth, and thus it is possible to obtain a high-resolution image.
Among the antennas as described above, the resistive dipole antenna has a small volume, and thus high-density arrangement becomes possible. In addition, since the resistive dipole antenna has the advantage that it can radiate ultra wideband signal with low distortion in the time domain, it has been actively used in the radar. However, its backward radiation and reception possibility still causes a problem.
In the rear of the antenna device, system hardware or an operator usually exists, and the electromagnetic signal that is radiated by the radar and then is reflected from such system hardware or operator acts as clutter to limit the performance of the radar system. In order to solve this problem, a metal reflective plate or a microwave absorber may be installed in the rear of the antenna device.
However, the metal reflective plate may change the waveform of the electromagnetic signal that is radiated by the radar and then is reflected from the target to change the antenna characteristic, and the microwave absorber may cause a problem in implementing the system due to its large volume.